Device and method for generating an electrical power supply in an electronic system with a variable reference potential

ABSTRACT

A method and device for generating a power supply voltage (Vf), referenced to a first reference potential ( 4 ), in an electronic system including an energizing source ( 3 ) connected to the first and second reference potentials ( 4, 5 ) so as to impart an AC voltage differential between the reference potentials ( 4, 5 ), wherein the device includes: (i) a source ( 10 ) for supplying AC voltage, which is referenced to the second reference potential ( 5 ), connected to the first reference potential ( 4 ), and encompasses the energizing source ( 3 ); and (ii) rectifying and filtering elements ( 1 ) connected, at the input thereof, to the first reference potential ( 4 ) and to the source ( 10 ) for supplying AC voltage, respectively, so as to generate, at an output ( 8 ), a power supply voltage (Vf) referenced to the first reference potential ( 4 ) by rectifying a voltage at the terminals of the source ( 10 ) for supplying AC voltage.

TECHNICAL FIELD

The present invention relates to a device for generating an electrical power supply in an electronic system with a variable reference potential.

The field of the invention is more particularly but non-limitatively that of electronic power supply devices.

STATE OF THE PRIOR ART

Generally, electronic systems are referenced with respect to a ground potential, which can be for example a voltage reference with respect to which the power supply voltages are fixed. This ground may or may not be connected to the earth.

In certain cases, it is necessary that electronic parts or sub-systems be referenced to potentials different from the ground potential of the overall system, and floating or variable with respect to the latter. This case is encountered for example in measurement systems, in order to be free from electrical interference noise sources.

Sometimes, the floating part is not totally separated from the remainder of the system by galvanic isolation, but it is floating or variable only in a range of frequencies, or about a working frequency.

Special arrangements are necessary in order to be able to electrically supply a floating sub-system and to transmit analogue and/or digital signals between this floating system and the part referenced to the ground potential.

This case is encountered for example in the document FR 2 756 048 by Rozière which discloses a capacitive measurement system. The detection circuit comprises a part that floats in a range of frequencies and of which the reference potential oscillates with respect to the ground of the overall system at an oscillation frequency.

The power supply voltages are transmitted to the floating part via inductance coils or choke coils placed in series on

the lines so as to present a high impedance at the oscillation frequency of the floating reference potential.

The same principle can be used for transmitting digital or analogue signals.

These digital or analogue signals can also be transmitted between the floating and non-floating parts by other known means such as differential amplifiers, optical couplers, or radio transmission means.

Electronic functions must often be produced in the form of integrated electronic circuits with minimal overall dimensions and electrical consumption. This is particularly true for the capacitive measurement systems which are increasingly used to produce touch-sensitive interfaces for portable systems (telephones, computers, etc).

In this context, the known means for transmitting signals and the power supplies between the floating and non-floating parts have undesirable drawbacks, such as large overall dimensions and high consumption.

These drawbacks are particularly important with regard to the electrical power supply of the parts that are floating parts or subjected to variable reference potentials. In fact, power supply sources are more easily available for the non-floating parts and it is necessary to transfer signals, that are substantially DC and of sufficient power, between the systems having different reference potentials. This involves the use of inductances (choke coils) or of DC/DC converters that are particularly disadvantageous for producing integrated circuits.

The purpose of the present invention is to propose a device and a method for generating an electrical power supply with a variable reference potential from a power source having another reference potential, without necessitating the use of disadvantageous electrical isolation components.

DISCLOSURE OF THE INVENTION

This objective is achieved with a device for generating a power supply voltage referenced to a first reference potential, in an electronic system comprising an excitation source connected to said

first and second reference potentials so as to impose an AC voltage difference between these reference potentials,

characterized in that it comprises moreover:

-   -   a source supplying an AC voltage referenced to said second         reference potential, connected to said first reference         potential, and encompassing said excitation source, and     -   rectifying and filtering means connected at the input thereof to         said first reference potential and to said AC voltage supply         source respectively, so as to generate, at an output, a supply         voltage referenced to said first reference potential by         rectification of a voltage at the terminals of the AC voltage         supply source.

The term “connected” must of course be interpreted in the sense that components connected to each other can be connected directly, through a direct electrical link, or connected via additional electrical or electronic components.

According to embodiments, the device according to the invention can comprise moreover:

-   -   an excitation source referenced to the second reference         potential;     -   an excitation source comprising a buffer referenced to the         second reference potential, connected at its output to the first         reference potential, and controlled at its input by an         oscillator referenced to said first reference potential;     -   rectifying and filtering means connected at their input to the         terminals of the excitation source or, if appropriate, to the         buffer of the excitation source;     -   rectifying and filtering means connected at their input to the         second reference potential, so as to generate at an output a         supply voltage referenced to the first reference potential by         rectification of the voltage at the terminals of an excitation         source referenced to the second reference potential.

The device according to the invention can comprise moreover an AC voltage supply source comprising at least one second AC voltage supply source connected to the second reference potential, and

rectifying and filtering means connected at the input to said second AC voltage supply source.

It can then comprise moreover an excitation source referenced to the first reference potential.

Thus, according to the embodiments, the excitation source can be referenced to the first reference potential. In this case, the AC voltage supply source according to the invention comprises at least one second AC voltage source referenced to the second reference potential, which supplies the major part of the power. The excitation source is then used as a return path for the current of this second AC voltage source.

The excitation source can also be referenced to the second reference potential. In this case, it can be used as the sole voltage source for the AC voltage supply source according to the invention. It can also be used in conjunction with a second AC voltage source connected to the second reference potential, in an active configuration in which its voltage contributes to the AC voltage supply source, or in a passive configuration (for example if the frequencies of the sources are very different) in which case it is used as a return path for the current of this second AC voltage source.

Finally, the excitation source can comprise a buffer referenced to the second reference potential, connected at its output to the first reference potential, and controlled at its input by an oscillator referenced to the first reference potential. This buffer can for example be produced by means of operational amplifiers. The buffer supplies the power necessary for the excitation of the first reference potential with respect to the second one, in accordance with the signal supplied by the oscillator. In fact it behaves as an excitation source referenced to the second reference potential.

In all cases, the excitation source is encompassed (or comprised or included) in the AC voltage supply source according to the invention because its presence is an element necessary for its correct operation.

In fact, these configurations are possible because the excitation source behaves substantially as a perfect voltage generator, also called a Thevenin generator. It makes it possible to impose an

AC voltage difference between the first and second reference potentials, whilst presenting a very low impedance to the supply current. This result could not be obtained without the presence of the excitation source.

When the excitation source comprises a buffer referenced to the second reference potential connected at its output to the first reference potential, it is this buffer which behaves at its output like a Thevenin generator placed between the first reference potential and, via the supply of the buffer, the second reference potential.

According to embodiments, the rectifying and filtering means can comprise:

-   -   switching means;     -   at least one diode inserted between the AC voltage supply source         and the output of the supply voltage;     -   a diode having a low threshold;     -   a Schottky diode, a germanium diode, etc.;     -   a filtering capacitor connected on the one hand to the first         reference potential and on the other hand to the output of the         supply voltage.

The device according to the invention can be produced using integrated electronics technologies.

According to another aspect, there is proposed an electronic capacitive measurement system comprising a first sub-system electrically referenced to a guard potential, a second sub-system electrically referenced to a ground potential, and an excitation source having terminals respectively connected to said guard and ground potentials so as to impose an AC voltage difference between these ground and guard potentials, this electronic capacitive measurement system comprising moreover a device according to the invention for generating a supply voltage referenced to said guard potential.

The electronic capacitive measurement system can comprise moreover a charge amplifier referenced to the guard potential and supplied by a device according to the invention for generating a supply voltage referenced to said guard potential.

According to yet another aspect, there is proposed a method for generating a supply voltage referenced to a first reference potential

in an electronic system comprising an excitation source connected to said first and second reference potentials so as to impose an AC voltage difference between these reference potentials,

This method comprising moreover the steps:

-   -   of generation of an AC supply voltage by means of an AC voltage         supply source referenced to said second reference potential,         connected to said first reference potential, and encompassing         said excitation source, and     -   of rectification of a voltage at the terminals of said AC         voltage supply source, with rectifying and filtering means         connected at their input respectively to said first reference         potential and to said AC voltage supply source, so as to         generate at an output of said rectifying and filtering means a         supply voltage referenced to said first reference potential.

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

Other advantages and characteristics of the invention will become apparent on examination of the detailed description of an embodiment which is in no way limitative, and the attached diagrams, in which:

FIG. 1 shows an embodiment of a device for generating supply voltage a according to the invention between electronic systems of which the reference potentials are connected by a periodic signal comprising a first embodiment of rectifying and filtering means and an AC voltage supply source comprising an excitation source and a second AC voltage source,

FIG. 2 shows an embodiment of a device for generating supply voltage according to the invention comprising a first embodiment of rectifying and filtering means and an AC voltage supply source comprising an excitation source,

FIG. 3 shows an embodiment of a device for generating supply voltage according to the invention comprising a second embodiment of rectifying and filtering means,

FIG. 4 shows an embodiment of a device for generating supply voltage according to the invention comprising a third embodiment of rectifying and filtering means,

FIG. 5 shows an embodiment of an electronic capacitive measurement system implementing a device for generating supply voltage according to the invention, and

FIG. 6 shows an embodiment example of an electronic capacitive measurement system of the prior art.

With reference to FIG. 1, the purpose of the present invention is to allow the generation of an electrical power supply Vf with a variable reference potential Of from a power source having another reference potential.

In particular, the invention makes it possible to avoid the use of electrical isolation components that are disadvantageous in terms of integration in integrated electronic circuits such as ASICs (Application Specific Integrated Circuits).

It is applied in electronic applications necessitating the interconnection of electronic systems D1, D2 of which the reference potentials 4, 5 are connected by a periodic AC signal generated by an excitation source 3. This AC signal can be of any form, for example sinusoidal, square or triangular.

This situation occurs, for example, in electronic measurement systems. According to a frequent but non-limitative configuration, the electronic system comprises:

-   -   a system D2 electrically referenced to the ground or to the         earth 5, which comprises the electrical power supply means of         the assembly, or is connected to an electrical power supply         network;     -   another electronic system D1 electrically referenced to a         variable reference potential 4, which comprises for example         electronic measuring means or high-sensitivity and/or low noise         detection means;     -   an AC voltage excitation source 3 which connects (directly or         indirectly) the ground 5 and the variable reference 4, in such a         way as to make the variable reference voltage 4 oscillate with         respect to the ground 5.

The electronic systems D1 and D2 are connected by electrical connections 2 which make it possible to convey, for example, digital or analogue signals. These electrical connections 2 are provided

with decoupling means 9 in order to provide electrical isolation between the reference potentials 4 and 5, at least in a range of frequencies. These decoupling means 9 can for example comprise inductances inserted in series on the lines or differential operational amplifiers. They can also comprise capacitors, which constitute an advantageous solution in terms of integration in a context of the production of circuits in the form of integrated circuits.

It is known to generate electrical supplies for the electronic system D1 having the variable reference potential 4 by transferring electrical supplies from the system D2 having the ground potential, for example through electrical connections 2 provided with decoupling means 9. In this case, these decoupling means 9 must be capable of allowing the power to pass though at low frequency, which involves the use of components such as inductances or transformers, which are disadvantageous in terms of integration in integrated circuits.

It is also known to use DC/DC converters but these are also disadvantageous in terms of overall dimensions in integrated circuits.

For the purpose of generating the variable potential 4, the excitation source 3 can be referenced either to this variable reference potential 4 or to the ground potential 5. It is then supplied, respectively, by a supply referenced to the variable reference potential 4 or to the ground potential 5.

However, as the electrical power supply sources are generally more easily available in one of the systems D1 or D2, it is preferable to use an excitation source 3 referenced to the corresponding reference potential 4 or 5. Thus, it is often preferable for the excitation source 3 to be referenced to the ground potential 5. It can then be supplied by a supply referenced to this same ground potential 5, which is more easily available and capable of providing an adequate electrical power.

According to an advantageous aspect of the invention, the excitation source 3 is used for producing an AC voltage supply source 10, capable of generating one or more power supply voltage(s) Vf referenced to the variable potential 4.

According to the embodiment shown in FIG. 1, the AC voltage supply source 10 comprises therefore the excitation source 3 and at least one second AC voltage source 11. The second AC voltage source 11 is connected to the ground potential 5. It is therefore connected, via the ground 5 or directly, to the excitation source 3. The device according to the invention also comprises rectifying and filtering means 1 which are connected at the input to the terminals of the AC supply source 10, and therefore inserted around the excitation source 3, between the electronic systems D1 and D2.

From the point of view of the rectifying and filtering means, the AC supply source 10 comprises therefore, in series, the excitation source 3 and the second AC voltage source 11.

The function of the excitation source 3 is to allow a return of the supply circuit through a connection between the variable reference potential 4 and the ground potential 5, without short-circuiting these reference potentials at the frequencies of the excitation signal of the excitation source 3. This effect is obtained as explained previously thanks to the Thevenin generator operation of the excitation source 3, which imposes the excitation signal between the variable 4 and ground 5 reference potentials, whilst having a low impedance.

Depending on the configurations, the excitation source 3 can contribute to a greater or lesser degree to the generation of the voltage of the AC power supply source 10. Basically, its contribution is that of a voltage source placed in series with the second AC voltage source 11. For example:

-   -   if the signals of the excitation source 3 and of the second AC         voltage source 11 are at close frequencies, their contributions         to the voltage of the AC power supply source 10 combine;     -   if the signals of the excitation source 3 and of the second AC         voltage source 11 are at very different frequencies, the signals         of the excitation source 3 can be rejected by filtering         components (capacitors for example) in the rectifying and         filtering means. This configuration makes it possible to         generate power supply voltages Vf referenced to the variable         reference potential 4 independent of the characteristics of the         signals of the excitation source 3, whilst making use of the         properties of the link that it provides between the ground 5 and         variable reference 4 potentials. Thus, it is possible for         example to modulate the amplitude of the excitation source 3         without modifying the supply voltage Vf which depends only on         the second AC voltage source 11.

The function of the rectifying and filtering means 1 is:

-   -   to rectify the signal of the AC power supply source 10, i.e. to         generate a supply voltage Vf with a non-zero mean value, from         the signal of the AC power supply source 10 which can have a         zero or any mean value;     -   to smooth the rectified signal in order to reduce the amplitude         of the voltage fluctuations.

According to an embodiment example shown in FIG. 1, they comprise:

-   -   a voltage rectifier component 6, connected to a terminal of the         AC power supply source 10. The output of this rectifier         component provides the supply voltage Vf, which is referenced to         the variable potential 4 and which is therefore usable for the         system D1. According to the embodiment shown in FIG. 1, this         component is a diode 6, for example one with a low threshold of         the Schottky type. The orientation of this diode 6 is in general         immaterial, in particular if the AC power supply source 10         supplies a symmetrical signal. In fact, depending on its         direction, it blocks the positive or negative alternations,         respectively, of the signal of the AC power supply source 10,         and thus determines the sign of the supply Vf;     -   a filtering component 7 which can be limited to a capacitor 7         respectively connected to the output 8 of the diode 6, at the         end opposite to that of the ground 5, and to the output of the         AC power supply source 10 connected to the variable reference         potential 4. The capacitor 7 smoothes the rectified signal         coming from the diode 6.

With reference to FIG. 2, the AC power supply source 10 can be constituted by the excitation source 3, referenced to the ground potential 5. The rectifying and filtering means 1 (identical in the example of FIG. 1 to those of FIG. 2) are then connected to the terminals of the excitation source 3.

In this way a device 1 is constituted rectifying the voltage of the excitation source 3 which is connected to the terminals of the latter according to an

arrangement that is inverted with respect to the conventional circuit diagrams of the prior art (since the diode 6 is in fact connected at its output to the ground 5 of the excitation source 3). However, as the active output of the excitation source 3 is also connected to the variable potential 4, it follows that there is thus generated, with a minimum of components that can be integrated easily, a rectified supply voltage Vf referenced to the variable potential 4 and available for the system that has the variable reference potential D1.

Voltage raising or lowering rectifying and filtering means 1, making it possible to adjust the supply voltage to the technical constraints of circuits whilst minimizing losses, can also be used in the context of the invention.

FIG. 3 shows an embodiment example in which the rectifying and filtering means 1 comprise a voltage raising device, for example known as a Schenkel voltage-doubling rectifier.

This embodiment can be used with different embodiments of the AC power supply source 10, which can comprise the excitation source 3 and optionally one or more AC voltage sources 11.

The voltage raising device comprises the diodes 20, 21 and the capacitor 22, arranged as shown in FIG. 2. It makes it possible, from a symmetrical or at least bipolar AC voltage source 11, to supply at its output 8 a supply voltage Vf referenced to the variable potential 4 of which the amplitude is of the order of the peak-to-peak amplitude of the signal of the source 11. The diodes 20, 21 are preferably low-threshold Schottky diodes.

The rectifying and filtering means 1 also comprise a filtering component 23 which can be limited to a capacitor 23 connected, respectively, to the output 8 of the diode 20 and to the output of the excitation source 3 connected to the variable reference potential 4. The capacitor 7 smoothes the rectified signal coming from the voltage raising device.

FIG. 4 shows an embodiment example in which the rectifying and filtering means 1 comprise a high-output voltage divider device.

This embodiment can be used with different embodiments of the AC power supply source 10, which can comprise the excitation source 3 and optionally one or more AC voltage sources 11.

The voltage dividing device comprises the diodes 30, 31 and the capacitors 32, 33, arranged as shown in FIG. 3. It makes it possible, from a single-pole AC voltage source 10 (i.e. oscillating between a maximum or minimum value of voltage and the reference potential 5), to supply at its output 8 a supply voltage Vf referenced to the variable potential 4 of which the amplitude is for example of the order of half of the peak-to-peak amplitude of the signal of the source 10 if the capacitors 32, 33 have the same value. The diodes 30, 31 are preferably low-threshold Schottky diodes.

The rectifying and filtering means 1 also comprise a filtering component 34 which can be limited to a capacitor 34 connected, respectively, to the output 8 of the diode 30, and to the output of the excitation source 3 connected to the variable reference potential 4. The capacitor 34 smoothes the rectified signal coming from the voltage-raising device.

According to variants,

-   -   an AC power supply source 10 can comprise a plurality of AC         voltage sources 11;     -   several supplies Vf can be produced from the same excitation         source 3, and/or the same AC power supply source 10;     -   any rectifying and filtering means 1 making it possible to         generate one or more supply voltages Vf referenced to the         variable potential 4 from an AC power supply source 10 can be         used in the context of the invention. They can comprise, in a         non-limitative way, charge transfer systems, charge pump         systems, voltage raising or attenuating systems, switches,         produced by the association of capacitors and diodes or by any         other means;     -   the rectifying and filtering means 1 can use any type of         switching means capable of allowing a rectification of the         signal of the AC power supply source 10. They can for example         comprise passive switches such as diodes only allowing signals         with a specified polarity to pass through,         Schottky diodes for reducing losses, or active analogue         switches, controlled for example by means of transistors;     -   the smoothing function can be carried out by equivalent         elements, such as parasitic capacitances and insofar as is         necessary for the requirements for using the AC supply voltage         Vf;     -   the signals of the AC voltage source or sources 11 and/or of the         excitation source 3 can be sinusoidal, square or of any other         shape;     -   the AC voltage source or sources 11 and/or the excitation source         3 can comprise a symmetrical bipolar oscillator supplying a         signal comprised between a positive value and a negative value,         or an asymmetrical single-pole oscillator supplying a signal         comprised between a maximum or minimum value and the reference         potential 5;     -   the alternative AC voltage source or sources 11 and/or the         excitation source 3 can be of analogue or digital type, for         example a direct digital synthesis (DDS) type;

Devices according to the invention can advantageously be used in a large variety of electronic systems which necessitate grounds 4, 5 at different potentials but not necessarily isolated.

The device according to the invention is particularly well suited for producing the power supply for the floating part (or the part with a variable reference potential) of a floating bridge capacitive measuring system such as described for example in the document FR 2 756 048 by Rozière. In fact, in this application, the detection circuit comprises a so-called floating part of which the reference potential, referred to as the guard potential, oscillates with respect to the ground of the overall system, or to the ground. The AC potential difference between the guard potential and the ground is generated by an excitation source. In the embodiments described in FR 2 756 048, the supplies of the part referenced to the guard are produced, in particular through DC/DC converters and/or inductance coils, from the supplies of the part referenced to the ground. As explained previously, these components are very disadvantageous in terms of integration in integrated circuits.

FIG. 5 shows a configuration example of a floating bridge capacitive measuring system such as described in the document FR

2 756 048, in capacitance measurement mode, to which has been added a power supply device according to the invention. The embodiment shown is, by way of non-limitative example, that of FIG. 1 or of FIG. 2. In order to make the notations consistent, it is considered that the capacitive bridge referenced to the guard corresponds to the system D1 of FIG. 1 and the part referenced to the ground or to the earth corresponds to the system D2.

This capacitive measuring system makes it possible to measure an item of capacitance information between at least one measuring electrode 40 and a target 41 connected to a potential different from the guard potential 4, such as for example the ground potential 5.

It comprises a floating part D1 referenced to a guard potential 4 oscillating with respect to the ground potential 5. An excitation source 3 referenced to the ground potential 5 provides the energising of the guard potential 4. A guard electrode 42 protects the measuring electrode 40. As it is at the same potential as the latter, it prevents the appearance of parasitic capacitances. The measuring electrode 40 is connected to a charge amplifier 43 which makes it possible to measure its capacitance.

Depending on the applications, the floating part of the electronics D1 can comprise other steps of processing the signal 44, in order for example to supply a signal representative of a distance between the measuring electrode 40 and the target 41. The system can moreover comprise several electrodes 40 having any geometry. It can also comprise a scanner inserted between the electrodes 40 and the charge amplifier 43, and making it possible to measure the capacitance of electrodes 40 sequentially.

The floating electronic system D1 and in particular the charge amplifier 43 are supplied by a device according to the invention, comprising an AC voltage supply source 10 based on the excitation source 3. This supply device comprises a rectifying diode 6 and a filtering capacitor 7, which deliver a supply voltage Vf referenced to the guard potential 4.

This floating bridge circuit shown in FIG. 5 or such as described in FR 2 756 048 makes it possible to be free of all parasitic capacitances, but this effect is obtained only if the components of the floating electronic system D1 are really powered in floating mode, hence the importance of generating high-quality power supplies for the floating part D1. In fact, in

this case, the measuring electrode 41, the guard electrode 42 and the reference Of of the power supply of the charge amplifier 43 are all approximately at the same floating AC potential, and practically no parasitic capacitance can appear between these elements.

FIG. 6 shows a capacitive measuring system with an active guard known in the prior art which also comprises a guard 4 energized by an excitation source 3. However, in this case the charge amplifier is supplied by a voltage source Vdc referenced to the ground 5. This circuit has the drawback of allowing the appearance of stray capacitances in particular between the inputs of the charge amplifier 43 and its supply Gnd. Moreover, this problem appears for all the components powered in this way, such as for example a scanner.

A floating bridge capacitive measuring system such as described in FIG. 5 makes it possible in particular to produce touch-sensitive or contactless interfaces for devices such as mobile telephones (smartphones), tablets, computers, proximity detectors, control pads or 3D capacitive cameras. The electrodes 40 can be transparent electrodes, for example made of ITO (tin-doped indium oxide), deposited on a display screen or a touch pad. They are then used for detecting the approach and/or contact of a command object 41 such as a finger.

In this case, the integration of the electronics in the form of integrated circuits or of ASICs having minimum overall dimensions is fundamental and the invention assumes all of its importance.

The energy that an excitation source 3 can provide for supplying the electronics D1 is often sufficient because present-day techniques make it possible to produce integrated circuits having very low energy consumption: it is possible to produce an integrated circuit where the floating electronics consume only a few mW. Moreover, the minimizing of electrical consumption is an important constraint for uses in portable devices.

In order to produce an integrated circuit with high capacitive performance, with capacitive leakages reduced to the minimum, it is preferable to integrate two separate components in the integrated circuit, one of which is for the floating part

D1 and the other of which is for the non-floating part D2. The two areas can also be separated by a shielding at the reference potential of the floating part.

The connection 2 between the output of the floating electronics D1 and the non-floating part D2 can be produced with coupling capacitors 9 using a digital transmission. The digital signals are preferably high rate signals, at high frequency, in order to use coupling capacitors 9 of low value so as not to overload the excitation source 3. It is also possible to use a differential amplifier powered by a power supply referenced to the ground 5 which retrieves the signals from the output of the floating electronics D1, whether they are analogue or digital.

The invention can also be used in very varied applications, among which can be mentioned in particular:

-   -   all types of capacitive floating bridge electronics, with all         types of signal processing such as filters, synchronous analogue         or digital demodulations, analogue/digital converters (ADC),         servo-control devices for producing bridges for measuring         capacitance C or inverse capacitance 1/C, switch controls for         sequentially scanning several electrodes, . . . ;     -   all measurement systems, capacitive or based on another physical         principle, comprising a part having a floating or variable         potential;     -   applications where it is necessary to limit stray AC currents         between systems and provide electromagnetic protection (EMC);     -   all applications requiring the interconnection of electronic         systems of which all the reference voltages or some of the         reference voltages are floating with AC potential differences;     -   all electronic systems comprising parts referenced to different         potentials, one energized with respect to the other by an         excitation source 3, these reference potentials being able to         all be floating or variable with respect to a ground or a earth,         and the excitation source 3 being able to be referenced to a         potential connected to a ground or a earth or floating with         respect to a earth or a ground.

Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention. 

1. Device for generating a power supply voltage (Vf) referenced to a first reference potential (4), in an electronic system comprising an excitation source (3) connected to said first and second reference potentials (4, 5) so as to impose an AC voltage difference between these reference potentials (4, 5), characterized in that it comprises moreover: a source supplying an AC voltage (10) referenced to said second reference potential (5), connected to said first reference potential (4), and encompassing said excitation source (3), and rectifying and filtering means (1) connected at the input thereof to said first reference potential (4) and to said AC voltage supply source (10) respectively, so as to generate, at an output (8), a supply voltage (Vf) referenced to said first reference potential (4) by rectification of a voltage at the terminals of the AC voltage supply source (10).
 2. Device according to claim 1, characterized in that it comprises moreover an excitation source (3) referenced to the second reference potential (5).
 3. Device according to claim 2, characterized in that it comprises moreover an excitation source (3) comprising a buffer referenced to the second reference potential (5), connected at its output to the first reference potential (4), and controlled at its input by an oscillator referenced to said first reference potential (4).
 4. Device according to claim 1, characterized in that it comprises moreover rectifying and filtering means (1) connected at their input to the terminals of the excitation source (3).
 5. Device according to claim 1, characterized in that it comprises moreover an AC voltage supply source (10) comprising at least one second AC voltage supply source (11) connected to the second reference potential (5), and rectifying and filtering means (1) connected at the input to said second AC voltage supply source (11).
 6. Device according to claim 5, characterized in that it comprises moreover an excitation source (3) referenced to the first reference potential (5).
 7. Device according to claim 1, characterized in that the rectifying and filtering means (1) comprise switching means (6, 20, 21, 30, 31).
 8. Device according to claim 1, characterized in that the rectifying and filtering means (1) comprise at least one diode (6, 20, 30) inserted between the AC voltage supply source (10) and the output (8) of the supply voltage (Vf).
 9. Device according to claim 1, characterized in that the rectifying and filtering means (1) comprise at least one diode (6, 20, 21, 30, 31) having a low threshold.
 10. Device according to claim 1, characterized in that the rectifying and filtering means (1) comprise moreover a filtering capacitor (7) connected on the one hand to the first reference potential (4) and on the other hand to the output (8) of the supply voltage (Vf).
 11. Device according to claim 1, characterized in that it is produced using integrated electronics technologies.
 12. Electronic capacitive measurement system comprising a first sub-system (D1) electrically referenced to a guard potential (4), a second sub-system (D2) electrically referenced to an ground potential (5), and an excitation source (3) having terminals respectively connected to said guard (4) and ground (5) potentials so as to impose an AC voltage difference between these ground (5) and guard (4) potentials, characterized in that it comprises moreover a device for generating a supply voltage (Vf) referenced to said guard potential (4) according to claim
 1. 13. Electronic capacitive measurement system according to claim 12, characterized in that it comprises moreover a charge amplifier (43) referenced to the guard potential (4) and supplied by a device for generating a supply voltage (Vf) referenced to said guard potential (4).
 14. Method for generating a supply voltage (Vf) referenced to a first reference potential (4) in an electronic system comprising an excitation source (3) connected to said first and second reference potentials (4, 5) so as to impose an AC voltage difference between these reference potentials (4, 5), characterized in that it comprises moreover steps: of generation of an AC supply voltage by means of an AC voltage supply source (10) referenced to said second reference potential (5), connected to said first reference potential (4), and encompassing said excitation source (3), and of rectification of a voltage at the terminals of said AC voltage supply source (10), with rectifying and filtering means (1) connected at their input respectively to said first reference potential (4) and to said AC voltage supply source (10), so as to generate at an output (8) of said rectifying and filtering means (1) a supply voltage (Vf) referenced to said first reference potential (4). 